Camera tube mesh clamped between dished annular members

ABSTRACT

An electron beam tube of the type having a fine conductive mesh adjacent a target is described, the fine mesh being clamped around its periphery between two annular members. An annular damping washer of flexible material is also clamped between the two members and extends inwards towards the picture area of the fine mesh. The two members are in addition dished away from one another and from the fine mesh in a region inwards of the clamping region so that the annular damping washer exhibits corrugations in the space between the fine mesh and the dished portion of the Clamping member which contacts the washer, the washer thereby contacting the fine mesh at a number of different places and restricting the degree to which the washer may lift away from the conductive mesh.

United States Patent Horton et al.

[ 1 CAIVIERA TUBE IVIESH CLAMPED BETWEEN DISHED ANNULAR NIEIVIBERSInventors: Laurence Henry Horton, Witham;

Peter Harvey Batey, Chelmsford, both of England [73] Assignee: EnglishElectric Valve Company Limited, Chelmsford, England [22] Filed: Oct. 15,1974 21 Appl. No.: 514,484

[451 Sept. 16, 1975 Carpenter et a1. 313/390 X Kawamura et a1 313/383[57 ABSTRACT An electron beam tube of the type having a fine conductivemesh adjacent a target is described, the fine mesh being clamped aroundits periphery between two annular members. An annular damping washer offlexible material is also clamped between the two members and extendsinwards towards the picture area of the fine mesh. The two members arein addition dished away from one another and from the fine mesh in aregion inwards of the clamping region so that the annular damping washerexhibits corrugations in the space between the fine mesh and the dishedportion of the Clamping member which contacts the washer, the washerthereby contacting the fine mesh at a number of different places andrestricting the degree to which the washer may lift away from theconductive mesh.

4 Claims, 2 Drawing Figures PATENTEUSEF 1 ems 31 106278 SHEET 2 [1F 2CAMERA TUBE MESH CLAIVIPED BETWEEN DISHED ANNULAR MEMBERS This inventionrelates to television and like camera cathode ray tubes and inparticular, though not exclusively, to vidicon camera cathode ray tubes.

Many camera cathode ray tubes include a fine conductive mesh adjacentthe scanned target of the tube. In a vidicon, the scanned target is alayer of photoconductive material on the inside surface of the frontface of the tube envelope and the fine conductive mesh usually referredto as the field terminating mesh is a short distance (e.g., 3millimetres) on the electron gun side of the target. In an imageorthicon, the scan target is a secondary electron emitting layer and themesh usually called the target mesh is very. closely adjacent thereto onthe side thereof remote from the electron gun.

A very serious defect experienced With tubes of this type is an effectwhich is commonly called microphony, this term having been adopted,possibly rather loosely, from analogy with microphonic efiects which areproduced in thermionic valves as a result of relative vibratorymovements of the electrodes thereof when they are subject to mechanicalshock or vibration.

Microphony in a tube of the kind described above, manifests itself in apicture reproduced from the output signals of the tube as a disturbingbackground of lines or striations.

In the specification of our U.K. Pat. No. 1,014,376 is described acamera tube in which, in order to reduce the effects of microphony, adamping washer, specifically an apertured mesh, is provided in contactwith the main mesh referred to above. In preferred embodiments of acamera tube in accordance with Pat. No. 1,014,376, the damping meshwasher has a rectangular aperture. Camera tubes in accordance with Pat.No. 1,014,376 have been found to provide a satisfactory degree ofprotection against the effects of microphony.

In many cases it is an operational requirement that the tube berotatable about its axis. This is so, for example, where the tube is tobe one of a number of tubes forming part of a colour television camera.In particular, tubes of the kind using a lead oxide target, such asthose known under the registered Trade Mark Leddicon, require to berotatable about their axis during the setting up of the camera. Thisrequirement of being rotatable about its axis tends to preclude the useof a damping washer having a rectangular aperture. If a damping washerwhich is annular in form is used, however, the washer tends to distortinwardly and lift away from the main mesh towards the inner periphery ofthe washer, thus reducing the effectiveness of the damping provided.

The present invention seeks to provide an improved camera tube having aconductive mesh adjacent the scanned target of the tube in which theeffects of this last mentioned difficulty are reduced.

According to this invention a television or like cam era cathode raytube having a fine conductive mesh adjacent the target of the tube isprovided wherein said fine conductive mesh is clamped around itsperiphery between two annular members and an annular washer of flexiblematerial is also clamped between said two members and in contact withsaid fine conductive mesh, said washer extending inwardly beyond theregion of clamping by said two members towards the useful picture areaof the fine conductive mesh and the inner regions of said two membersbeing dished beyond the region of clamping away from each other and saidfine conductive mesh, whereby the dished portion of that clamping memberin contact with said washer acts to restrict the degree to which theportion of said washer beyond the region of clamping may lift away fromsaid fineconductive mesh so as to cause said damping washer to exhibitcorrugations in the space between the fine conductive mesh and thedished portion of that clamping member in contact with the washer, sothat said washer in said space contacts at different places said fineconductive mesh and the dished portion of that clamping member.

Preferably said washer extends up to the edge of the useful picture areaof the fine conductive mesh. Preferably again said washer comprises arelatively heavy copper mesh.

To quote a practical example, whereas said fine conductive mesh may havea thickness of 0.0003 inch and have 750 holes per inch, the heavy coppermesh used for the washer may have a thickness of 0.0006 inch and have500 holes per inch.

Normally said two clamping members, the fine conductive mesh and saidwasher are secured together by spot welding around the outer peripheryof the assembly.

The invention is further described with reference to the accompanyingdrawings in which,

FIG. 1 is a part sectioned broken away view of the target end of onevidicon camera cathode ray tube in accordance with the presentinvention, and

FIG. 2 is a part cut away perspective view of the arrangement of fineconductive mesh, damping washer and clamping members of a typicalvidicon in accordance with the present invention.

Like references are used for like parts in FIGS. 1 and 2.

Referring to FIG. 1, the glass envelope of the tube is shown at 1.Within the glass envelope 1, may be seen the focusing electrode 2 of thetube. Extending beyond the focusing electrode 2 is a metal member 3 intowhich a support member 4 fits. Support member 4 is secured Within metalmember 3 by means of a plurality of tabs of which one is shown at 5.Member 3 is spaced from focusing electrode 2 by a metal spacer 6.

Support member 4 carries t e fine conductive field terminating mesh 7 ofthe vidicon and for that reason is commonly referred to as the meshring. The photoconductive target of the vidicon is represented at 8.

The thin conductive mesh 7 is held in tension across the mesh ring orsupport member 4 by the clamping action of this last mentioned memberand a further clamping member 9.

Because space: 6, member 3 and member 4 are all of conductive material,in this example a vidicon, the thin conductive mesh 7, is operated at apotential which is the same as the operating potential of the focusingelectrode 2. In other words, this example of vidicon is of the so-calledintegral mesh type.

As so far described the vidicon is as well known per se and is prone tosuffer from microphony as previously described.

In accordance with the present invention, in order to reduce the effectsof such microphony, a flexible damping washer 10, consisting of a heavycopper mesh of thickness 0.0006 inch and having 500 holes per inch isalso clamped between the two members 4 and 9 in contact with the fineconductive mesh 7. The members 4 and 9 with the mesh 7 and Washer 10 aresecured together by spot welding around the outer periphery of theassembly. The copper mesh washer 10 in this example is between the fineconductive mesh 7 and the clamping member 9. An alternative is to fitthe copper mesh washer 10 between the fine conductive mesh 7 and themesh support ring 4. In either case, the members 4 and 9 are dished awayfrom each other beyond the region of clamping 11 provided by the twomembers 4 and 9, as shown. The depth of the recess formed by dishing ineach case is typically 0.005 inch. The copper mesh washer 10 extendsinwardly beyond the region of clamping 1 1 up to the edge of the usefulpicture area of the thin metal mesh 7, defined by the edge 12 of theclamping member 9.

As best seen from FIG. 2, the dished portion of clamping member 9 actsto restrict the degree to which the portion of mesh washer 10 beyond theregion of clamping 11 would otherwise tend to distort and lift away fromthe fine conductive mesh 7. This causes the mesh washer 10 to exhibitcorrugations in the space, formed by dishing, between the fineconductive mesh 7 and the dished portion of clamping member 9, so thatin places the mesh washer 10 contacts the dished portion of clampingmember 9, whilst at other places the mesh washer 10 contacts the fineconductive mesh 7.

The effect of dishing the members 4 and 9 is to permit any vibrations inthe fine conductive mesh 7 to continue into the space between the dishedportions of the members 4 and 9. The copper mesh washer 10, beingflexible, tends to follow movements of the thin conductive mesh 7, but,being relatively dense and being relatively reluctant to move due to thedistributative contact it has with the dished portion member 9, tends tosuppress such vibratory movements and thus reduce the effects ofmicrophony.

We claim:

1. A television or like camera cathode ray tube having a fine conductivemesh adjacent the target of the tube wherein said fine conductive meshis clamped around its periphery between two annular members and anannular washer of flexible material is also clamped between said twomembers and in contact with said fine conductive mesh, said washerextending inwardly beyond the region of clamping by said two memberstowards the useful picture area of the fine conductive mesh and theinner regions of said two members being dished beyond the region ofclamping away from each other and said fine conductive mesh, whereby thedished portion of that clamping member in contact with said washer actsto restrict the degree to which the portion of said washer beyond theregion of clamping may lift away from said fine conductive mesh so as tocause said damping washer to exhibit corrugations in the space betweenthe fine conductive mesh and the dished portion of that clamping memberin contact with the washer, so that said washer in said space contactsat different places said fine conductive mesh and the dished portion ofthat clamping member.

2. A tube as claimed in claim 1 and wherein said washer extends up tothe edge of the useful picture area of the fine conductive mesh.

3. A tube as claimed in claim 1 and wherein said washer comprises arelatively heavy copper mesh.

4. A tube as claimed in claim 1 and wherein said two clamping members,the fine conductive mesh and said washer are secured together by spotwelding around the outer periphery of the assembly.

1. A television or like camera cathode ray tube having a fine conductivemesh adjacent the target of the tube wherein said fine conductive meshis clamped around its periphery between two annular members and anannular washer of flexible material is also clamped between said twomembers and in contact with said fine conductive mesh, said washerextending inwardly beyond the region of clamping by said two memberstowards the useful picture area of the fine conductive mesh and theinner regions of said two members being dished beyond the region ofclamping away from each other and said fine conductive mesh, whereby thedished portion of that clamping member in contact with said washer actsto restrict the degree to which the portion of said washer beyond theregion of clamping may lift away from said fine conductive mesh so as tocause said damping washer to exhibit corrugations in the space betweenthe fine conductive mesh and the dished portion of that clamping memberin contact with the washer, so that said washer in said space contactsat different places said fine conductive mesh and the dished portion ofthat clamping member.
 2. A tube as claimed in claim 1 and wherein saidwasher extends up to the edge of the useful picture area of the fineconductive mesh.
 3. A tube as claimed in claim 1 and wherein said washercomprises a relatively heavy copper mesh.
 4. A tube as claimed in claim1 and wherein said two clamping members, the fine conductive mesh andsaid washer are secured together by spot welding around the outerperiphery of the assembly.